Add new code

Signed-off-by: Carlos Maiolino <[email protected]>

4 files changed, 164 insertions, 0 deletions

diff --git a/PGU/OLD/chapter3/exit b/PGU/OLD/chapter3/exit
new file mode 100644
index 0000000..a70d0fd
--- /dev/null
+++ b/PGU/OLD/chapter3/exit
diff --git a/PGU/OLD/chapter3/exit.s b/PGU/OLD/chapter3/exit.s
new file mode 100644
index 0000000..632ebed
--- /dev/null
+++ b/PGU/OLD/chapter3/exit.s
@@ -0,0 +1,70 @@
+# A useless program, which the only thing this shit does is call exit syscall
+# The exit status code can be read using
+
+# `echo $?` on shell, which will show the exit status of the last program run.
+
+
+# %eax holds the system call number
+# %ebx holds the return status
+
+
+# Assembler directives (or pseudo-operations).
+#
+# Everything starting with a period, is an instruction to the assembler itself.
+# They are handled by the assembler program, not actually executed by the
+# computer.
+
+# .section command breaks the program down into sections.
+
+# .data section lists any memory storage which will be needed for data
+.section .data
+
+# .text section lists the program instructions
+.section .text
+
+# Instructs the assembler that _start is "important to remember".
+# _start is a symbol, which is going to be replaced by something else either
+# during assembly or linking
+
+# Symbols are generally used to mark locations of programs or data, so you can
+# refer to them by name instead of by location number
+
+# .globl means that the assembler should not discard this symbol after assembly,
+# because the linker will need it.
+
+# _start is a special symbol that always needs to be marked with .globl, because
+# it marks the location of the start of the program.
+
+# If the program is not marked this way, when the computer loads the program, it
+# won't know where to begin running the program.
+
+.globl _start
+
+# Defines the value of _start label. Label == a symbol followed by a colon.
+# Labels defines a symbol's value.
+
+# Labels tell the assembler to make the symbol's value be wherever the next
+# instruction or data element will be.
+
+_start:
+
+# different from the book, I'm using x86_64 instructions and its registers, so,
+# instead of using %eax and %ebx, I'm using %rax and %rbx directly. The movl
+# instruction needed to be changed to movq (move quad) to adapt to the 64-bit
+# registers
+# mov: (move) 16-bit
+# movl: (move long) 32-bit
+# movq: (move quad) 64-bit
+
+#ins $(val), (dest) == immediate mode
+movq $1, %rax		# Move value 1 into %eax register
+			# %eax will hold the syscall number
+			# by the linux's calling convention
+
+movq $100, %rbx		# Move value 0 into %ebx register
+			# %ebx will hold the exit() syscall
+			# argument.
+
+int $0x80		# Interrupt 0x80 will wake up the kernel
+			# execute the syscall loaded into %eax
+
diff --git a/PGU/OLD/chapter3/max.s b/PGU/OLD/chapter3/max.s
new file mode 100644
index 0000000..6ebc906
--- /dev/null
+++ b/PGU/OLD/chapter3/max.s
@@ -0,0 +1,42 @@
+# Given a list of X numbers, find the maximum number of the list and use it as
+# the argument of exit() syscall
+
+# %rbx holds the maximum number through the whole scanning process
+# %rax holds the current element being examined
+# %rdi holds the currend position in the list
+# zero marks the end of the list
+
+# Data section, now containing some statically created data
+.section .data
+
+# Just a label to refer to the first item in the list
+data_items:
+	# "Type" of memory location to be reserved. In quotes because it just
+	# says how many bytes should be reserved to each item, not the 'type'
+	# itself
+	# Reserves 10 '8byte' (quad) slots consecutive in memory,
+	.quad 3,10,9,230,66,77,23,66,12,69,0
+
+.section .text
+
+.globl _start
+
+_start:
+	movq $0, %rdi
+	movq data_items(, %rdi,8), %rax
+	movq %rax, %rbx
+
+	start_loop:
+		cmpq $0, %rax
+		je loop_exit
+		incq %rdi
+		movq data_items(,%rdi,8), %rax
+		cmpq %rbx, %rax
+		jle start_loop
+		movq %rax, %rbx
+		jmp start_loop
+
+
+	loop_exit:
+		movq $1, %rax
+		int $0x80
diff --git a/PGU/OLD/chapter3/min.s b/PGU/OLD/chapter3/min.s
new file mode 100644
index 0000000..9179be7
--- /dev/null
+++ b/PGU/OLD/chapter3/min.s
@@ -0,0 +1,52 @@
+# This code has been originally copied from max.s
+
+# It has been modified to:
+#	- Find the smallest value, instead of the largest
+#	- Use Start/End addresses to delimit the boundaries of the number list
+#
+# %rax - holds the current element being examined
+# %rbx - Holds the smallest number
+
+.section .data
+
+# This version has 2 labels, one to point to the start of the list, and another
+# to point to the address right after it, so we can use it to search the list
+# boundary.
+
+data_items:
+	.quad 234,10,9,230,66,77,23,66,101,69,100
+data_end:
+
+.section .text
+
+.globl _start
+
+_start:
+
+# Using immediate mode with a label, will give you the ADDRESS of the
+# instruction/data it points to. Once the label itself contains an ADDRESS, the
+# immediate mode will give you the ADDRESS itself.
+
+# Using direct mode with a label, will give you the DATA into the address the
+# label points to. Once the label itself contains an address, the direct mode,
+# as expected will give you the DATA into the address pointed by the label.
+	movq	$data_items, %rax
+	cmpq	$data_end, %rax			# We need this check here in case
+	je	exit_loop_empty			# the items list is empty
+	movq	(%rax), %rbx
+
+	loop_start:
+		addq	$8, %rax		# We are using QuadWords, so 8 bytes
+		cmpq	$data_end, %rax
+		je	exit_loop
+
+		cmpq	(%rax), %rbx
+		jle	loop_start
+		movq	(%rax), %rbx
+		jmp	loop_start
+
+	exit_loop_empty:
+		movq	$255, %rbx
+	exit_loop:
+		movq	$1, %rax
+		int	$0x80